Thermal Control Design for the MODIS Instrument

Santa Barbara Research Center is currently under contract from NASA Goddard Space Flight Center to design and build the MODerate resolution Imaging Spectroradiometer (MODIS) for launch in 1998 on the EOS-AM spacecraft. MODIS is a remote sensing instrument incorporating state-of-the-art multi-spectral imaging and calibration technology. Two cooled infrared (IR) focal planes and two room-temperature visible and near infrared focal planes are used to gather imaging data in 36 discrete spectral bands between 0.41 and 14.4 μm. A passive radiative cooler is employed to achieve a nominal IR focal plane operating temperature of 85K.

To meet mission objectives, band-to-band registration of ±0.2 pixel and radiometric calibration accuracy better than 1% within the thermal region and 5% within the reflectance region must be maintained over a five-year instrument design life. This places significant demands on the thermal design which must provide a stable operating environment with minimal temperature gradients and thermoelastic distortion. Advanced engineering materials including beryllium and graphite/epoxy are used extensively in the design along with various passive thermal control techniques to optimize performance.

This paper presents an overview of MODIS thermal control design features along with a summary of analytical performance predictions for the overall system and for thermally critical subsystems such as the passive cryogenic radiative cooler. Thermal engineering challenges are discussed along with corresponding design solutions.